The present invention relates to a device for generating an indicator signal which is representative of an AC signal amplitude input to the device.
The present invention also relates to the use of such an indicator signal, to a base station, a handset and to a receiver or transceiver provided with such a device and to a network including a base station and handset.
Such a device is known from our European patent application EP-A-0 152 985. The device disclosed therein is a high-frequency amplifier arrangement for generating an indicator signal which is representative of an AC signal amplitude in the device. For the known device to generate an indicator signal which is used to control the gain in amplifier stages in the device an, IF signal on input Si1 is being AM detected to reveal the automatic gain control (AGC) indicator signal. The AGC uses a broadband AM detector to cope with the full frequency range of the AC signal. To achieve that goal, the known device is not a low power consuming device and is therefore not suitable for application in an environment where a low power consumption is required such as in portable or mobile devices, such as telephones, base stations, handsets, and pagers.
It is an object of the present invention to provide a low power consuming device over a broad frequency range, which device is capable of being used as an RSSI (Received Signal Strength Indicator), such as in AGC. Thereto the device according to the present invention is characterized in that the device comprises at least one semiconductor whose DC bias current is representative of said AC signal amplitude, and means for deriving the indicator signal from the DC bias current. A low DC bias current flows through the semiconductor if a zero AC signal amplitude is input and the DC bias current is related to the input AC signal amplitude. This reduces the power consumption of the device according to the present invention as no DC current is spilt. It is a further advantage of the device according to the invention that the means for deriving the indicator signal can be embodied as averaging or low-pass means which are both simple and require little power. In addition it is an advantage that a variety of practical implementations embodying the principle of a DC bias current representing the AC signal amplitude can be realised.
The device can advantageously be used for controlling the gain in an amplifier circuit, such as in a receiver or transceiver in a base station and/or handset in a network, such as a communication network for minimizing gain to reduce the power consumption and in particular for minimizing RF power supplied to the air in order to furthermore minimize mutual disturbance between communicating parties in the network.